Recent developments in airplane manufacturing technology have enabled the fabrication of airplane fuselage sections with unprecedented precision. U.S. Pat. No. 5,560,102 entitled "Panel and Fuselage Assembly" issued on Oct. 1, 1996 to Micale and Strand discloses a breakthrough in fabrication technology which eliminates the need for expensive and error-prone hard tooling for fabricating airplane fuselage sections. This invention made it possible, for the first time in the history of airplane manufacturing, to build airplane fuselages to a specified tolerance without shims by building the individual panels within tolerance.
One of the steps of the process of the '102 patent noted above is to accurately position stringer clips in the channel of a stringer and to match drill holes through the stringer sidewalls and the stringer clip for subsequent fastener installation operations. An end effector for the machine tool shown in the U.S. Pat. No. 5,560,102 patent is shown in U.S. Pat. No. 5,127,139, entitled "Stringer Clip End Effector" issued on Jul. 7, 1992 to Peter McCowin and Hugh Schlosstein for performing these clip placement and drilling operations.
The end effector of the '139 patent performed well, accurately placing and drilling stringer clips in the stringers, but it used a significant amount of machine tool time in the assembly cell. To increase the capacity of the assembly cell for other operations as described in the '102 patent, the stringer/clip placement and drilling operations were removed from the assembly cell and performed in a dedicated machine that was invented and designed for that purpose. This dedicated machine is disclosed in U.S. Pat. No. 5,477,596 entitled "Stringer Clip Placement and Drilling" issued to Peter McCowin and Hugh Schlosstein.
The end effector of the '139 patent and the machine of the '996 patent were designed for straight stringers in the constant contour section of the airplane, shown in the left hand side of FIG. 1. However, the nose and the aft end of an airplane fuselage, shown in the right side of FIG. 1, have a compound contour that requires curved stringers. The webs of the stringer clips must be aligned on and parallel to the station planes, shown as a series of vertical lines in FIG. 1, since the airplane fuselage frame at each station plane is attached to the stringer clip webs aligned on that station plane, as shown in FIG. 2. In the constant contour sections of the fuselage, the orientation of all the clip webs is at a constant 90.degree. to the axis of the stringer since the stringers lie at 90.degree. to the frames. In the compound contour sections of the fuselage, however, the angle that the clip webs make with the stringer axis is different at different station planes since they must remain parallel to the station plane even though the stringer curves to conform to the compound contour of the fuselage. Moreover, the relative position of the pairs of holes drilled through the stringer sidewall and the stringer clip is different for the clips at different station planes, so in any automated system for placing and drilling the stringer clips in curved stringers, there must be some provision for accommodating these differences.
Thus, there exists a need for an automated apparatus and process for placing stringer clips at desired locations in desired orientations along a curved stringer for a compound contour section of an airplane fuselage and holding the clip at the desired location at the desired orientation while holes for subsequent fastener operations are drilled.